Added btMultiBodyPoint2Point, it can be used between btMultiBody vs btMultiBody or btMultiBody vs btRigidBody

Allow picking of btMultiBody, using a btMultiBodyPoint2Point constraint, with limited strength to avoid adding too much energy to the system (= blowup)
Add btMultiBodyJointMotor, it can be used in combination with joint limit (just add the joint limit after the motor, to avoid jitter)

src/BulletDynamics/Featherstone/btMultiBodyConstraintSolver.cpp

@@ -764,6 +764,7 @@ void btMultiBodyConstraintSolver::convertContacts(btPersistentManifold** manifol
 	for (int i=0;i<m_tmpNumMultiBodyConstraints;i++)
 	{
 		btMultiBodyConstraint* c = m_tmpMultiBodyConstraints[i];
+		m_data.m_solverBodyPool = &m_tmpSolverBodyPool;
 		c->createConstraintRows(m_multiBodyNonContactConstraints,m_data,	infoGlobal);
 	}